The radiolabeled antibody delivery system utilizing a quality control test kit developed during Phase I of this grant, will be clinically tested in patients with colorectal cancer. The kit measures the percentage of immunoreactive radioactivity of radiolabeled antibody or antibody fragments intended for patient use. The patients will be those who are scheduled for a surgical resection following the administration of I-125 labeled monoclonal antibodies. During surgery, a gamma detection probe will be used to guide the surgeon to putative sites of tumor deposit. A dot immunoassay will be used in addition to immunohistochemical straining to predict whether antigens recognized by the monoclonal antibody are expressed by the tumor. After antibody radiolabeling, the antibody will be tested using the quality control device to measure its tumor binding ex vivo in the presence and absence of the patient's serum. A clinical trial will be used to test the hypothesis that efficacy of antibody targeting can be improved if the antibodies are patient- specific, with selection based on a measure of their binding to biopsy samples and again to the biopsy sample after radiolabeling. The antibody delivery system, if validated, is intended for us e with both immunotherapy and radiotherapy antibody pharmaceuticals to solid tumors.